Genetic background of spontaneous autoimmune thyroiditis in the obese strain of chickens studied in hybrids with an inbred line.

To determine the number and function of genes which are responsible for spontaneous autoimmune thyroiditis (SAT) in the obese strain (OS) of chickens we crossed birds of this strain (B15/B15) with those of the inbred CB line (B12/B12). The progeny was analyzed for autoantibodies to thyroglobulin (TgAAb) and for histopathological changes in the thyroid glands. In F1 (OS X CB) hybrids only those animals which derived from CB mothers had circulating TgAAb, the progeny from the reverse combination female OS X male CB was negative. Since the disease is not inherited by OS males only, we conclude that maternal TgAAb, which are transferred from the egg yolk to the embryo, might prevent the immune system of the F1 chickens from TgAAb formation via blocking or eliminating the respective antigens. Those F1 hybrids which have high TgAAb levels in the serum show only little or no thyroiditis. Together with other observations, these data lead to the conclusion that the thyroid gland of the F1 hybrids is not susceptible to TgAAb. This supports previous findings that a genetically determined thyroid abnormality is a prerequisite for the full development of SAT. The low degree of SAT in backcross (F1 X OS) animals and F2 hybrids suggests that several genes are involved in the disease. MHC typing of these generations revealed that the B haplotype affects the time of SAT onset.